This invention relates to a combined ladder or stepladder levelling device with locking foot assembly which can be used so that ladders and stepladders can be safely used on non-level ground.
The problems associated with the use of ladders etc. on uneven or sloping ground are well documented with many patent applications having been made in an attempt to get over the problems involved. Yet even with the wealth of technical innovation in this area, there are still no effective ladder levelling devices on the market. The present invention overcomes the difficulties by integrating, ease of use, simple operation and minimum projections from the lines of the ladder stiles combined with low manufacturing/assembly costs and capability of being easily fitted to a very wide range of ladder types.
It is known to have extensions slidably mounted within the hollow stiles of a ladder which can be pulled out and locked in position and by this means the length of each stile of a ladder can be independently varied.
However these are difficult to use requiring awkward or difficult adjustments to be made whilst trying to erect and position the ladder. Another problem is that with ladders commonly made of extruded aluminium any ratchet or similar device made from similar materials is very prone to wear in use and can consequently fail. Harder materials are either too costly or suffer from corrosion problems.
I have devised an improved ladder stile extension device allowing a ladder to be correctly positioned whatever the slope of the ground and which is easier to use in practice.
According to the invention there is provided a device for adjusting the length of a stile of a ladder which device comprises a ladder extender able to be slidably attached to a stile of a ladder in which device there is a ratchet means which comprises a first rack fixed relative to the stile and a second rack attached to the extender, whereby the teeth of the first and second racks can engage with each other in use to prevent the extender from retracting, there being a disengagement means being able to be operated to disengage the teeth of the first and second racks from each other, which disengagement means incorporates a contact means which can engage with the teeth of the second rack, with the contact means being in contact with and passing over the teeth of the second rack when there is relative opening movement between the first and second racks, but which does not operate to disengage the teeth when an outside force is exerted on the end of the extender in an attempt to retract it.
The disengaging means can incorporate a roller attached to and adjacent to the first rack, which roller, by engaging with the teeth of the second rack lifts the first rack clear and disengages the opposing sets of teeth during the extending operation.
Alternatively the disengaging means can comprise a pad of low friction material which, by engaging with the teeth of the second rack, lifts the first rack clear and disengages the opposing sets of teeth during the extending operation and, being of low friction, minimises the wear on the teeth as it passes over them.
Preferably on the lower end of the extender is mounted a foot component that allows movement in two directions, maintaining the adequate transfer of loads to the ground whatever the slope of the ground, with up to 10 to 12 degrees of crossfall accommodated.
Preferably the first rack has an opposing lever arm as an extension and the rack is pivotally mounted about a pivot whereby pressure adjacent the end of the lever arm will cause the rack to rock or rotate about the pivot and disengage the teeth of the first rack from the teeth of the second rack.
With a number of teeth in the first rack at close centres, small incremental movement of extender""s telescopic action can be achieved.
Preferably the main components of the device will be constructed of extruded sections. The design of the extruded sections allows the incorporation of the lever arrangement generally without special machining operations.
A conventional ratchet design arrangement, although naturally allowing incremental opening movement would result in excessive wear on the ratchet teeth, particularly to the teeth located on the lever arm closest to the centre of rotation. To prevent this and allow the use of soft aluminium extrusions to form both the rotating lever arm and the teeth, a roller arrangement or low friction device (plastic block) is built into the lever, close to the pivot that automatically lifts the opposing teeth clear during movementxe2x80x94extending the device, but which, as with a simple ratchet prevents the reverse motion closing the device.
A compression or other flat spring acting on the lever arm provides a positive pressure to ensure the positive interlocking of the two sets of teeth. An operating knob is preferably mounted externally to the device, either connected directly to the lever arm or via a connecting rod, to allow manual operation, extension or retraction as well as providing a safety catch arrangement, preventing accidental retraction of the device whilst in service.
The use of a rotating lever could be substituted by a device that maintains the first rack in a position perpendicular or square with the second racket reducing uneven wear of the components.
Generally the upper unit fixed relative to the ladder stile is constructed of a hollow extrusion which totally surrounds and provides stability to the lower movable unit which is formed from either an H or C shaped extrusion. Greater strength can be provided to the movable unit when in the extended position by either one or two further H or C shaped extrusions that interlock with the main telescopic extrusion to form effectively a hollow unit rather than an open sided component. This also serves to protect the ratchet components from the ingress of dirt etc.
All pins spindles and the like within the upper or lower units are restrained in their longitudinal direction i.e. transverse or perpendicular to the line of the main extrusions by either the main extrusions or other further extrusions linked to same thereby avoiding the use of nuts or end clips to maintain accurate positioning and alignment.
Many of the auxiliary components within the device can be made by cutting suitably shaped aluminium extrusion into short lengths 10 mm-30 mm long thereby utilising the accuracy and intricacy capable, with the extrusion process, without resorting to excessive machining and other expensive metal fabrication processes. Should production quantities be such so as to warrant greater initial capital expense then some of these subsidiary components could be formed in cast aluminium or of high strength plastics by injection moulding.
The whole device can be mounted, either within the lower end stile section of a hollow aluminium ladder, or attached to the side of ladders whether constructed of timber or aluminium. Generally there would be one such device mounted to the lower ends of each ladder stile (two in total) and four such devices mounted to the lower ends of the legs of stepladders. Though when attached to the side of stile or leg of the units can be made removable allowing a 50% reduction in numbers required for effective and safe operation.
When a ladder is used on uneven or sloping ground and one of the stiles fails to make proper contact with the ground causing the ladder to lean sideways, making it therefore unstable and unsafe. With this device fitted, levelling of the ladder is very easily achieved by simply extending the inner lower component of the device with the person""s foot while holding the ladder stiles with both hands in the correct vertical orientation. With the retracting/safety knob (safety knob) in the released position, the internal ratchet arrangement allows small incremental adjustment of foot position without the operator having to release hand grip on the ladder. When fully adjusted the ladder is then safe to use, and to ensure that the operating lever handle is not accidentally knocked, the safety knob is rotated into the locked position, preventing any further telescopic action in either direction.
With the device mounted internally within the stiles of a hollow aluminium ladder below the lowest tread it is possible to obtain approximately 70 mm of vertical movement, enough to adjust for a greater than 10 degree cross fall. When mounted externally to ladder or stepladder greater adjustment is possible as the device can be made longer using the same basic extrusions and components. In these circumstances it would be possible to obtain vertical adjustment in excess of 250 mm allowing the ladder or stepladder to be used in safety, on steps and the like.
Load from the ladder is transferred to the ground via a foot unit incorporating a shaped spindle that permits the foot to be rotated sideways in addition to the usual fore aft movement thereby accommodating slopes and crossfalls. A locking device can be included within the spindle that enables the orientation of the foot to be fixed or locked at any angle within the operating range. This locking action also prevents the feet from vibrating when being transported on the roof of vehicles.
When the ground is soft the surface area of the feet can be increased with a slip on boot.
Retraction of the device is achieved either under the action of a return spring when one is fitted or manually when no such spring is installed. The safety knob is first released and then depressed releasing the sets of ratchet teeth allowing the moving section to retract under the action of the return spring, or to be pushed back manually.
A plastic material pad can be included on the rotating lever that bears when fully depressed on the vertical ratchet assembly thereby acting as a simple brake. preventing retraction in an uncontrolled manner.
Preferably the release mechanism can be operated by a person""s foot so that, when utilised, the user can hold the ladder with his hands and slide the extender out to the desired length e.g. by pressing down on the foot of the extender until contact with the ground is achieved.
To retract the device the release mechanism can again be operated by a person""s foot whilst holding the ladder and allowing weight of the ladder to push back the extender until the foot on the opposing stile reaches the ground. When the ladder is laid horizontally the device can be pushed back by hand.